Method for selecting a cellular network

ABSTRACT

A method performed by a mobile device of selecting a cellular network entails activating a cellular radio transceiver, scanning a most recently used frequency list of radiofrequency channels most recently used by the cellular radio transceiver of the mobile device, scanning a likely frequency list of likely radiofrequency channels available at a plurality of locations where activation of cellular radio transceivers commonly occurs, and selecting the cellular network by identifying one of the radiofrequency channels as a usable channel.

TECHNICAL FIELD

The present disclosure relates generally to wireless communications and,in particular, to cellular network selection techniques.

BACKGROUND

When the user of a mobile device travels to a foreign country by air,the user typically shuts off the mobile device or activates “airplanemode” prior to taking off in order to deactivate the cellular radiotransceiver and possibly radio transceivers of other radio accesstechnologies (RAT) such as Wi-Fi®. Upon reaching the destination whenusage of cellular radio is permitted, the user may decide to reactivatethe cellular radio transceiver. Upon reactivation of the cellular radiotransceiver, a 3GPP-compliant mobile device generally known as a UserEquipment (UE) initially attempts to find the last registered publicland mobile network (R-PLMN) or equivalent public land mobile network(E-PLMN) to perform a Location Registration by scanning all RATs withwhich the mobile device is capable of communicating. If no cellularradio coverage is available from the last registered PLMN (which is thecase when the user travels to a foreign country), then the mobile deviceinitiates a network scan to attempt registration on other PLMN/RATcombinations according to a 3GPP-specified order such as starting withthe RAT priority specified in Home PLMN (HPLMN) and Equivalent Home PLMN(EHPLMN) Elementary File (EF) on a subscriber identity module (SIM) oruniversal subscriber identity module (USIM) followed by User ControlledPLMN Selector with Access Technology EF followed by Operator ControlledPLMN Selector with Access Technology EF and so on (as specified by 3GPPTS 23.122).

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present technology will becomeapparent from the following detailed description, taken in combinationwith the appended drawings, in which:

FIG. 1 is a depiction of a mobile device capable of implementing a rapidnetwork selection technique;

FIG. 2 is a flowchart outlining a method of selecting a cellularnetwork;

FIG. 3 is a flowchart of a specific method of selecting a cellularnetwork;

FIG. 4 is an extension of the flowchart of FIG. 3; and

FIG. 5 is a flowchart of a simplified method of selecting a cellularnetwork.

It will be noted that throughout the appended drawings, like featuresare identified by like reference numerals.

DETAILED DESCRIPTION

Because of the large number of radio frequency (RF) bands supported oneach RAT by a typical 3GPP UE (mobile device), it may take quite a whilefor a typical 3GPP-compliant mobile device to select a cellular networkthat provides service to the user after landing in a foreign country.This delay in providing service to the user may be exacerbated in somespecific mobile device implementations that always trigger a networkscan for the home network after switch on if the Last RPLMN SelectionIndication EF on the SIM/USIM is enabled by the network operator. As aresult, a typical 3GPP-compliant mobile device may take up to 2-4minutes before it is able to provide service to the user after airplanemode is turned off upon arriving in a foreign country. This leads to apoor user experience. The user is also subjected to a similar experiencewhen the user returns home especially with a SIM that does not have theLast RPLMN Selection Indication EF configured.

With the ever-increasing number of radiofrequency (RF) bands and RATsthat a typical 3GPP-compliant mobile device expected to support, thiswill get worse. For example, a mobile device may support Long TermEvolution (LTE) RF bands 1, 2, 3, 4, 5, 6, 8, 13, 17, 20, 25, 26, 28,39, 40, 41, Universal Mobile Telecommunication System (UMTS) RF bands 1,2, 4, 5/6, 8 and quad-band Global System for Mobile Communications(GSM). A typical mobile device implementation of network scan afterpower on involves performing one or more scans of Most Recently Used(MRU) cellular systems followed by a full exhaustive scan of allsupported RF bands on all supported RATs (i.e. a full RAT/band scan).The MRU list stores cell identification parameters of a fixed number oflast used cells in a non-volatile memory of the mobile device, e.g. theMRU list may comprise 10 UMTS cells and 10 LTE cells and cellidentifiers could be the PLMN identifier and associated downlink UTRAAbsolute Frequency Number (UARFCN) as defined in 3GPP TS 25.101 for UMTScells or downlink E-UTRA Absolute Frequency Number (EARFCN) as definedin 3GPP TS 36.101 for LTE cells. MRU scans on specified frequencies(UARFCN/EARFCN) are quite fast compared to exhaustive scan of allfrequencies within a given band hereafter called full band scans. Theduration of full band scan which is much longer and can vary dependingon the bandwidth of the spectrum of the band (e.g. 10 MHz vs. 75 MHz)and the presence of signals from other RATs within the spectra that maylead to false alarms while performing full scan assuming a particularRAT (e.g. presence of GSM signals during UMTS RAT scan). In general, MRUscans are quite effective when the user remains in the user's homenetwork as the likelihood of the mobile device still being in thecoverage of one of the last visited home cells is quite high; however,it does not help much when the user travels to a foreign country becausethere will not be any MRU entry for any cell from any foreign PLMN orwhen the user travels back home after visiting a foreign country as inthis case the MRU list is likely to be filled with visiting PLMNentries. There are also other scenarios when the MRU scan is noteffective e.g. if the user decides to change SIM, e.g. a subscriber of anetwork operator X1 may decide to switch to a new SIM that belongs to anetwork operator Y1 after landing in the country Y and switch back tohis/her home SIM (i.e. SIM X1) after returning home; in both cases(going abroad and coming back home), the current MRU contents may nolonger be relevant as the MRU entries represent the networks associatedwith the SIM prior to SIM switch. An improved method for selecting acellular network is thus highly desirable.

On activation of a cellular radio transceiver of a mobile device, it isdesirable for the mobile device to find a cellular network channelquickly in order to provide service to the end user. However, mobiledevices today need to scan an ever-growing set of cellular RF bands andRATs. For example, a cellular radio transceiver of a mobile device mayoperate on one or more cellular RF bands per RAT. For example, for LTE,these may be bands 1, 2, 3, 4, 5, 7, 8, 13, 17, 20, 25, 26, 28, 39, 40,41 (i.e. on 2100, 1900, 1800, 1700, 850, 2600, 900, 700, 700, 800, 1900,800, 700, 1900, 2300, 2500 MHz, respectively). For example, for HSPA+,bands 1, 2, 4, 5/6, 8 (i.e. 2100/1900/1700/850/900 MHz, respectively)may be used. For example, a quad-band GSM/GPRS/EDGE transceiver may usebands at the frequencies of 850/900/1800/1900 MHz. Scanning throughthese various bands can take a significant amount of time to completewhile also depleting the battery. A method to expedite cellular networkselection is therefore highly desirable.

The present specification discloses a method, computer-readable mediumand mobile device that expedite cellular network selection. In general,the network is selected by scanning a most recently used frequency listand a likely frequency list composed of the most likely or probablefrequencies available a plurality of locations where transceiveractivation occurs most commonly, e.g. at airports where the userdisables airplane mode upon landing that reactivates cellular radiotransceiver. In general, instead of performing multiple successive scansof most recently used (MRU) frequencies or a MRU scan followed by a fullband/RAT scan or just a full band/RAT scan, it is much more effective ifa focused scan is performed on a set of likely deployed frequencies inconjunction with the MRU frequencies when the cellular radio transceiveris re-activated, e.g. when airplane mode is disabled. The likelyfrequencies can be selected in a prioritized order based on the statusof service prior to turning airplane mode on, usage/change of SIM/USIMwhen airplane mode is turned off and/or various other criteria which aredescribed below.

Accordingly, in general terms, one aspect of the present disclosure is amethod performed by a mobile device of selecting a cellular network.This method entails activating a cellular radio transceiver, scanning amost recently used frequency list of radiofrequency channels mostrecently used by the cellular radio transceiver of the mobile device,scanning a likely frequency list of likely radiofrequency channelsavailable at a plurality of locations where activation of cellular radiotransceivers occurs, and selecting the cellular network by identifyingone of the radiofrequency channels as a usable channel.

Another aspect of the present disclosure is a computer-readable mediumcomprising instructions in code which when loaded into a memory andexecuted by a processor of a mobile device cause the mobile device toactivate a cellular radio transceiver, scan a most recently usedfrequency list of radiofrequency channels most recently used by thecellular radio transceiver of the mobile device, scan a likely frequencylist of likely radiofrequency channels available at a plurality oflocations where activation of cellular radio transceivers occurs andselect the cellular network by identifying one of the radiofrequencychannels as a usable channel.

Yet another aspect of the present disclosure is a mobile device having aprocessor coupled to a cellular radio transceiver for activating thecellular radio transceiver and a memory coupled to the processor forstoring a most recently used frequency list of radiofrequency channelsmost recently used by the cellular radio transceiver of the mobiledevice and for storing a likely frequency list of likely radiofrequencychannels available at a plurality of locations where activation ofcellular radio transceivers commonly occurs. The processor is configuredto scan the most recently used frequency list and the likely frequencylist and to select the cellular network by identifying one of theradiofrequency channels as a usable channel.

The details and particulars of these aspects of the disclosure will nowbe described below, by way of example, with reference to the drawings.

The likely frequency list is composed of frequencies (channels) that areavailable at locations where RF transceiver activation is most likely tooccur. In one implementation, the locations where RF transceiveractivation occurs most commonly are airports. In other words, RFtransceivers are frequently disabled before a flight and thenreactivated on landing. Upon arrival in another city or country, themobile device must scan for a network which can provide roaming service.

Given that the cellular radio frequency bands are assigned by theregulatory body in a given country and a given network operator isallocated only a certain portion of the frequency bad, it is quitecommon that there are some common frequencies that are deployed in everyairport of the country that the network operator serves. In fact, forRATs that require wide RF bandwidth such as FDD LTE which may have 20MHz system bandwidth, the number carrier frequencies that can bedeployed is quite small compared to a RAT that requires much smaller RFbandwidth such as GSM. In addition, some RF bands such 700-MHz bands arelimited in bandwidth; as a result, there can be only a very limitednumber of carrier frequencies that can be deployed in these bands. Forexample, LTE band 13 and 17 have bandwidths of 10 and 12 MHz,respectively, and are used by North American network operators who havedeployed just a single 10-MHz FDD LTE carrier frequency thus making thecentre frequency of band 13 or band 17 the same across all locations inthe country. Some examples are tabulated below to show the UTRA AbsoluteRadio Frequency Channel Number (UARFCN), where UTRA stands for UMTSTerrestrial Radio Access and the Evolved-UTRA Absolute Radio FrequencyChannel Number (EARFCN) deployment in UMTS WCDMA (Wideband Code DivisionMultiple Access) and LTE FDD (Frequency Division Multiplexing) cellsrespectively by network operators in various US airports:

Network US airports Operator RAT IAD BOS EWR ORD X1 LTE- EARFCN_(X11)EARFCN_(X11) EARFCN_(X11) EARFCN_(X11) FDD EARFCN_(X12) EARFCN_(X13)UMTS- UARFCN_(X11) WCDMA UARFCN_(X12) UARFCN_(X12) UARFCN1_(X2)UARFCN_(X13) UARFCN_(X13) UARFCN_(X13) X2 LTE- EARFCN_(X21) EARFCN_(X21)EARFCN_(X21) EARFCN_(X21) FDD EARFCN_(X22) EARFCN_(X23) X3 LTE-EARFCN_(X31) EARFCN_(X31) EARFCN_(X31) EARFCN_(X31) FDD EARFCN_(X32)

In the above table the carrier and radio access technology are shown forthe following airports (which are selected solely by way of example):Washington Dulles International Airport (IAD), Logan InternationalAirport (Boston), Newark Liberty International Airport (EWR), ChicagoO'Hare International Airport (ORD).

The following table shows the UARFCN and EARFCN deployment in variousCanadian airports, notably in Ottawa (YOW), Toronto (YYZ), Montreal(YUL) and Vancouver (YVR).

Network Canadian Airports Operator RAT YOW YYZ YUL YVR Y1 LTE-EARFCN_(Y11) EARFCN_(Y11) EARFCN_(Y11) FDD EARFCN_(Y12) EARFCN_(Y13)EARFCN_(Y14) UMTS- UARFCN_(Y11) UARFCN_(Y11) UARFCN_(Y11) UARFCN_(Y11)WCDMA UARFCN_(Y12) UARFCN_(Y13) Y2 LTE- EARFCN_(Y21) EARFCN_(Y21)EARFCN_(Y21) EARFCN_(Y21) FDD EARFCN_(Y22) UMTS- UARFCN_(Y21)UARFCN_(Y21) UARFCN_(Y21) WCDMA UARFCN_(Y22) UARFCN_(Y22) UARFCN_(Y22)

As shown above, the US network operator X1 deploys a common LTE band 17EARFCN_(X11) in LTE cells that are deployed in all major airports in theUS; similarly Canadian network operator Y1 deploys a common UMTS band 5UARFC_(Y11) in UMTS cells in all major airports in Canada. Airports areonly one example of locations where cellular transceiver activationcommonly occurs.

As part of one implementation, a frequency list named “Home NetworkLikely Frequency List” is created for each network operator thatrepresents the frequency number (ARFCN/UARFCN/EARFCN) of most likelydownlink centre frequency across all the RATs—the list is ordered basedon likelihood of occurrence of such frequencies in all major airports.The list may be generated via various methods or combination of methods,e.g. a frequency list may be hardcoded in mobile device software, builtby the device as it discovers frequencies in home network, downloaded tothe device in response to a list update trigger, etc. Such a trigger maybe time-dependent, location-dependent, based on usage patterns,predicted travel, user command or any other condition that defines atrigger. The data may be pushed to the device or pulled. Examples ofsuch lists are shown below:

Home Network Likely LTE UMTS Frequency Network EARFCN UARFCN List IndexOperator List List 1 Y1 EARFCN_(Y11), UARFCN_(Y11), EARFCN_(Y12),UARFCN_(Y12) 2 Y2 EARFCN_(Y21), UARFCN_(Y21), EARFCN_(Y22) UARFCN_(Y22),UARFCN_(Y23) 3 X1 EARFCN_(X12), UARFCN_(X11), EARFCN_(X12) UARFCN_(X12),EARFCN_(X13) UARFCN_(X13), UARFCN_(X14) 4 X2 EARFCN_(X21), UARFCN_(X21),EARFCN_(X22) UARFCN_(X22), UARFCN_(X23)

Based on the information specified in various EFs (such as PLMNSelector, User Controlled PLMN Selector, Operator Controlled PLMNSelector EFs) on SIM/USIM that provides preferred roaming partners in agiven country, another frequency list name “Roaming Network LikelyFrequency List” is constructed to assist scanning for most likelyroaming networks. Using this information, frequencies of different PLMNsin a given foreign country are prioritized; e.g. if SIM/USIM of OperatorX1 indicates that Network Operator Y1 is preferred over Network OperatorY2 in Country Y, then home network likely frequencies of NetworkOperator Y1 appear before Network Operator Y2 in Roaming Network LikelyFrequency List that is constructed for Network Operator X1.

The following Roaming Network Likely Frequency List may be created asfollows:

Roaming Network Likely Frequency List Network Indices of Home NetworkLikely Frequency Operator List of roaming partners Y1 Index 3 (i.e. HomeNetwork Likely Frequency List of X1) Y2 Index 4 (i.e. Home NetworkLikely Frequency List of X2) X1 Index 1 (i.e. Home Network LikelyFrequency List of Y1) Index 2 (i.e. Home Network Likely Frequency Listof Y2) X2 Index 2 (i.e. Home Network Likely Frequency List of Y2)

As a further embodiment, Roaming Network Likely Frequency List for agiven carrier comprises multiple RAT-specific lists—each onerepresenting all likely frequencies on a given RAT such as GSM/EDGE,UMTS-WCDMA, UMTS-TDSCDMA, LTE-FDD, LTE-TDD etc.

The Roaming Network Likely Frequency List may also include frequenciesthat are common amongst a number of network operators in differentcountries. In general, there may be multiple Roaming Network LikelyFrequency Lists, one for each region (e.g. Americas, Europe, MiddleEast, Asia, Africa, Oceania, etc.). The scan order among variousregional lists may be prioritized based on various factors such as aninitial location of the user, user's travel history, etc.

The likely frequency list is most efficiently stored directly in amemory of the mobile device or it may be stored in an external memorydevice accessible by the mobile device without cellular connectivity,e.g. accessible by universal serial bus (USB), near field communication(NFC), Wi-Fi®, Bluetooth®, or any suitable wired or wirelessdata-transfer interface. The rapid network-selection method may beimplemented by a mobile device which include a wireless communicationsdevice, tablet, personal digital assistant, cell phone, smart phone,smart watch, smart wearable accessory, gaming device or any otherportable electronic device or portable communication device.

FIG. 1 is a depiction of one example of a mobile device capable ofperforming a rapid network selection. This mobile device, which isgenerally designated by reference numeral 100, includes a processor 110and memory 120, 130 for executing one or more applications. The memorymay include flash memory 120 and/or random access memory (RAM) 130.Other types or forms of memory may be used.

As depicted by way of example in FIG. 1, the mobile device 100 includesa user interface 140 for interacting with the mobile device and itsapplications. The user interface 140 may include one or moreinput/output devices, such as a display screen 150 (e.g. an LCD or LEDscreen or touch-sensitive display screen), and may optionally include akeyboard or keypad. The user interface may also include an optical jogpad and/or a thumbwheel, trackball, track pad or equivalent.

As depicted by way of example in FIG. 1, the mobile device 100 mayinclude a cellular radio transceiver 170 for communicating with otherdevices. The cellular radio transceiver 170 enables wirelesscommunication with one or more base stations over a cellular wirelessnetwork using cellular communication protocols and standards for bothvoice calls and packet data transfer such as GSM, CDMA, GPRS, EDGE,UMTS, LTE, etc. Once the desired cellular network is identified, themobile device 100 connects to the cellular network via a basetransceiver station (BTS), base station controller (BSC), Serving GPRSSupport Node (SGSN), and Gateway GPRS Support Node (GGSN). In an LTEimplementation, the mobile device connects via eNode B (base station),mobility management entity (MME) and serving gateway (SGW).

The mobile device 100 may include a Subscriber Identity Module (SIM)card 112 or Universal Subscriber Identity Module (USIM) for GSM-typedevices or a Re-Usable Identification Module (RUIM) card for CDMA-typedevices. For the purposes of this specification, the term SIM shallinclude a USIM. The RF transceiver 170 may include separate voice anddata channels.

The mobile device 100 may also include one or more ports for wiredconnections, e.g. USB, HDMI, FireWire (IEEE 1394), etc.

The mobile device 100 optionally includes a speech-recognition subsystemthat has a microphone 180 for transforming voice input in the form ofsound waves into an electrical signal. Optionally, the mobile device 100may include a speaker 182 and/or an earphone jack.

The mobile device 100 optionally includes a position-determiningsubsystem such as a global navigation satellite system (GNSS) receiver,for example a Global Positioning System (GPS) receiver 190 (e.g. in theform of a chip or chipset) for receiving GNSS (e.g. GPS) radio signalstransmitted from one or more orbiting GNSS (e.g. GPS) satellites.

The mobile device 100 includes a Wi-Fi transceiver 192 (which may, insome embodiments, be just a Wi-Fi receiver) for receiving a Wi-Fi signaltransmitted by a Wi-Fi access point, router, adapter or hotspot.Although Wi-Fi® is a registered trademark of the Wi-Fi Alliance, itshall be identified simply as “Wi-Fi” in this specification. Wi-Fiencompasses the IEEE 802.11 standard and all its drafts and amendments.

The mobile device 100 optionally includes a Bluetooth® transceiver 194,and/or a near-field communications (NFC) chip. The mobile device 100 mayalso optionally include a transceiver for WiMax™ (IEEE 802.16), atransceiver for ZigBee® (IEEE 802.15.4-2003 or other wireless personalarea networks), an infrared transceiver or an ultra-widebandtransceiver.

Optionally, the mobile device may include other sensors like a digitalcompass 196 and/or accelerometer 198. Other sensors may include a tiltsensor, gyroscope or equivalent.

The processor 110 of the mobile device 100 (which is coupled to thecellular radio transceiver 170 via a data bus) activates the cellularradio transceiver in response to a trigger, e.g. a user command ordetection of a condition. The memory 120, 130, which is coupled to theprocessor 110, stores a most recently used (MRU) frequency list 200 ofradiofrequency channels most recently used by the cellular radiotransceiver of the mobile device. The memory 120, 130 also stores alikely frequency list (LFL) 210 of likely radiofrequency channelsavailable at a plurality of locations where activation of cellular radiotransceivers commonly occurs. The processor 110 is configured to scanthe most recently used frequency list and the likely frequency list andto select the cellular network by identifying one of the radiofrequencychannels as a usable channel, i.e. an RF channel that can be used by themobile device to communicate with a base transceiver station (BTS) orNode B.

An overview of one rapid network-selection method is described withreference to FIG. 2. As depicted in the flowchart of FIG. 2, the methodentails steps, acts or operations of activating (300) a cellular radiotransceiver, scanning (310) a most recently used frequency list ofradiofrequency channels most recently used by the cellular radiotransceiver of the mobile device, scanning (320) a likely frequency listof likely radiofrequency channels available at a plurality of locationswhere activation of cellular radio transceivers commonly occurs, andselecting (330) the cellular network by identifying one of theradiofrequency channels as a usable channel. The usable channel meansany pair of uplink and downlink frequencies (e.g. as defined by anAFRCN) over which the mobile device can communicate with a base stationtransceiver. In one embodiment, the likely frequency list includes onlyone ARFCN per location. In another embodiment, the likely frequency listincludes more than one ARFCN per location. The actual ARFCN and thenumber of ARFCN's stored per location may be dynamically changed by themobile device software or pushed to the device via various forms ofdevice provisioning.

The step of activating the cellular RF transceiver triggers the scanningfor a usable channel, i.e. causes the device to perform a rapid networkselection scan. The activating step may be any one of the following:powering on the mobile device, turning on the RF transceiver, disablingan airplane mode, disabling a bedside mode, returning from anout-of-coverage area or any event that causes the RF transceiver tosearch for a network.

The method may be further refined by taking into consideration whetherthe mobile device was roaming when the RF transceiver was deactivatedand/or whether a SIM card has been swapped.

In some instances, a mobile user may swap a home SIM card for a foreigncountry SIM card to minimize or avoid roaming charges. The user may thenreplace the foreign country with the home country SIM card uponreturning home. The most recently used (MRU) list may be different foreach SIM card's Home PLMN.

The method may entail determining whether the mobile device was roamingwhen the cellular radio transceiver was deactivated. If the mobiledevice was roaming when the cellular radio transceiver was deactivated,the mobile device scans a roaming network likely frequency list. If, onthe other hand, the mobile device was not roaming when the cellularradio transceiver was deactivated, the mobile device scans a homenetwork likely frequency list. In other words, in this particularimplementation, there are distinct home and roaming likely frequencylists. These lists may be stored together or separately. The home androaming likely frequency lists may be stored in any suitable database ordata structure.

As shown by way of example in the specific implementation presented inFIGS. 3 and 4, if the mobile device was roaming when the cellular radiotransceiver was deactivated, the mobile device scans the most recentlyused frequency list and the home network likely frequency if public landmobile network (PLMN) information stored in a subscriber identity module(SIM) does not match the PLMN information stored on the device upondeactivation of the transceiver. Alternatively, the mobile device scansthe most recently used frequency list and the roaming network likelyfrequency list if the PLMN information in the SIM matches the PLMNinformation stored upon deactivation of the transceiver.

In the specific implementation of the method shown in FIG. 3 and FIG. 4,the method is initiated when the RF transceiver is deactivated, e.g.when airplane mode is enabled (at step 400) by a user of the mobiledevice. In response to the deactivation of the transceiver, the mobiledevice stores PLMN information and roaming status data at step 410, e.g.SimPlmnAtAirplaneModeEntry=SIM HPLMN prior to radio off andRoamingStatusAtAirplaneModeEntry=True/False in device memory. If themobile device was roaming when airplane mode was entered, the roamingstatus is set to true. Otherwise, the roaming status is set to false,i.e. the device is not roaming.

At step 420, the airplane mode is turned off, causing the cellular radiotransceiver to be activated and to search for a network to providecellular service.

At step 430, the mobile device checks the stored roaming status todetermine whether the mobile device was roaming when the cellular radiotransceiver was deactivated in step 400. If the mobile device was indeedroaming, then the PLMN in the SIM is compared (at step 440) with thestored PLMN information. If there is a match, then scanning proceeds atstep 450 in the following order: (1) a scan of the MRU associated withthe PLMN of the current SIM; (2) a second scan of the MRU associatedwith the PLMN of the current SIM; (3) a scan of the Roaming NetworkLikely Frequency List associated with the SIM HPLMN; (4) a full RAT/bandscan. If the PLMN information does not match, then it implies there ischange of SIM and scanning is performed as per step 460 as follows: (1)a scan of the MRU list associated with the PLMN of the previous SIM; (2)a scan of the MRU list associated with the PLMN of the current SIM ifsuch an MRU list exists; (3) a scan of theHomeNetworkLikelyFrequencyList associated with the SIM HPLMN; (4) a fullRAT/band scan.

If the mobile device was not roaming (as determined by the mobile deviceat decision block 430), then the method flow proceeds as shown in FIG.4. As shown in FIG. 4, the mobile device then determines (at decisionblock 470) whether the PLMN information in the SIM matches the storedPLMN information at the time airplane mode was activated (“Does PLMN ofSIM=SimPlmnAtAirplaneModeEntry?”). The mobile device then determines ifthe PLMN information in the SIM matches the PLMN information stored onthe device upon deactivation. If there is a mismatch, then it indicatesthat the user has changed the SIM from a previous SIM to a new SIM andthe mobile device performs (at step 480) the scans in the followingorder until a usable channel is found: (1) a scan of an MRU listassociated with the PLMN of the previous SIM/USIM; (2) a scan of the MRUlist associated with the PLMN of the new SIM if such an MRU list exists;(3) a scan of a Home Network Likely Frequency List associated with thePLMN of the new SIM; (4) a scan of a Roaming Network Likely FrequencyList associated with the PLMN of the new SIM; and (5) a full RAT/bandscan. If there is a match determined at step 470, the mobile deviceperforms (at step 490) the scans in the following order until a usablechannel is found: (1) a scan of the MRU list associated with the PLMN ofthe current SIM, i.e. the SIM currently in the mobile device since noSIM swap has occurred; (2) a scan of the MRU list associated with thePLMN of the current SIM for the second time to provide time-domaindiversity; (3) a scan of the Roaming Network Likely Frequency Listassociated with the PLMN of the current SIM); (4) a scan of the HomeNetwork Likely Frequency List associated with the PLMN of the currentSIM; and (5) a full RAT/band scan.

FIG. 5 depicts a simplified method for network selection. As shown byway of example in FIG. 5, the simplified method is initiated when the RFtransceiver is deactivated, e.g. when airplane mode is enabled (at step500) by a user of the mobile device. In response to the deactivation ofthe transceiver, the mobile device stores PLMN information at step 510,e.g. SimPlmnAtAirplaneModeEntry=SIM HPLMN prior to radio off. Unlike themethod of FIGS. 3-4, the method of FIG. 5 does not need to determinewhether the device was roaming when airplane mode was entered. At step520, the airplane mode is turned off). At step 530, the mobile devicedetermines whether the PLMN information in the SIM matches the PLMNinformation stored in the device when airplane mode is disabled. Ifthere is a mismatch, then it indicates that the user has changed the SIMfrom a previous SIM to a new SIM and the mobile device performs (at step540) the scans in the following order until a usable channel is found:(1) a scan of the MRU list associated with the PLMN of the previousSIM/USIM; (2) a scan of the MRU list associated with the PLMN of the newSIM if such an MRU list exists; (3) a scan of the Home Network LikelyFrequency List associated with the PLMN of the new SIM; (4) a scan ofthe Roaming Network Likely Frequency List associated with the PLMN ofthe new SIM; and (5) a full RAT/band scan. If there is a matchdetermined at step 530, the mobile device performs (at step 550) thescans in the following order until a usable channel is found: (1) a scanof the MRU list associated with the PLMN of the current SIM; (2) a scanof the MRU list associated with the PLMN of the current SIM for thesecond time to provide time-domain diversity; (3) a scan of the RoamingNetwork Likely Frequency List associated with the PLMN of the currentSIM; (4) a scan of the Home Network Likely Frequency List associatedwith the PLMN of the current SIM; and (5) a full RAT/band scan.

The example of entering and exiting airplane mode depicted in FIGS. 3-5is presented solely to illustrate one way of deactivating andreactivating the cellular radio transceiver. The methods of FIGS. 3-5may be performed using any other deactivation and reactivation techniqueincluding, for example, manually turning off and on the cellular radiotransceiver, or powering down the mobile device and then powering up themobile device. The methods may be used for scenarios when the mobiledevice has experienced an extended loss of wireless coverage or a longperiod without battery power.

From the foregoing, it is to be noted that any of the above methods mayinvolve defining a PLMN/SIM-specific list of MRU frequencies that arestored in the mobile device for searching. The mobile device may store aplurality of such lists that are specific to each PLMN/SIM combination.

In the implementations depicted in FIGS. 3-5, the processor of themobile device is configured to detect a change in SIM (or USIM) at thetime the cellular radio transceiver is activated.

In a further implementation, the mobile device requests an updatedlikely frequency list in response to detecting that the mobile devicehas arrived at an airport. Detecting that the mobile device may be doneby comparing GPS coordinates against a database of known airportlocations. A calendar application or travel application may also be usedto provide an indication that the user of the mobile device is planningto take a flight. The updated list may also be downloaded as part of thepower down sequence or an RF transceiver shutdown sequence or inresponse to enabling the airplane mode or other mode that deactivatesthe cellular RF transceiver.

In a further implementation, the mobile device is configured to learn ordiscover (i.e. obtain) the likely frequency list by monitoring availablechannels at the plurality of locations. In a variant, the mobile devicemay share learned channel data with other mobile devices via a server orvia a peer-to-peer (P2P) platform. The channel data may also specify thereceived signal strength at the location (e.g. at the airport).

In a further variant, the frequency channels in the likely frequencylist may be prioritized based on user travel patterns, based on eventsstored by a calendar application or based on travel data stored by atravel application. For example, the user may travel to Fort Lauderdale,Fla. once per month. By noting this pattern, the mobile device canprioritize the frequencies to begin the search with the channelavailable at Fort Lauderdale International Airport (FLL). In anothervariant, an upcoming destination for the user may be determined byparsing e-mail, text message (e.g. SMS or MMS), social network posts, orother such content for names of destinations. For example, an e-mail ortext message stating “See you in Fort Lauderdale!” may be used by themobile device to determine that the next destination is probably FortLauderdale. In that case, the mobile device may prioritize the channelsto commence with the channel at Fort Lauderdale International Airport(FLL).

Any of the methods disclosed herein may be implemented in hardware,software, firmware or any combination thereof. Where implemented assoftware, the method steps, acts or operations may be programmed orcoded as computer-readable instructions and recorded electronically,magnetically or optically on a fixed, permanent, non-volatile ornon-transitory computer-readable medium, computer-readable memory,machine-readable memory or computer program product. In other words, thecomputer-readable memory or computer-readable medium comprisesinstructions in code which when loaded into a memory and executed on aprocessor of a computing device cause the computing device to performone or more of the foregoing method(s).

A computer-readable medium can be any means that contain, store,communicate, propagate or transport the program for use by or inconnection with the instruction execution system, apparatus or device.The computer-readable medium may be electronic, magnetic, optical,electromagnetic, infrared or any semiconductor system or device. Forexample, computer executable code to perform the methods disclosedherein may be tangibly recorded on a computer-readable medium including,but not limited to, a floppy-disk, a CD-ROM, a DVD, RAM, ROM, EPROM,Flash Memory or any suitable memory card, etc. The method may also beimplemented in hardware. A hardware implementation might employ discretelogic circuits having logic gates for implementing logic functions ondata signals, an application-specific integrated circuit (ASIC) havingappropriate combinational logic gates, a programmable gate array (PGA),a field programmable gate array (FPGA), etc.

The use of the terms “a” and “an” and “the” and similar referents orarticles in this specification are to be construed to cover both thesingular and the plural, unless otherwise indicated or clearly impliedby the context. The terms “comprising”, “having” and “including” are tobe construed as open-ended terms (i.e. meaning “including, but notlimited to,”) unless otherwise noted.

This disclosure has been described in terms of specific embodiments,implementations and configurations which are intended to be examplesonly. Persons of ordinary skill in the art will appreciate, having readthis disclosure, that many obvious variations, modifications andrefinements may be made without departing from the inventive concept(s)presented herein. The scope of the exclusive right sought by theApplicant(s) is therefore intended to be limited solely by the appendedclaims.

The invention claimed is:
 1. A method, performed by a mobile device, ofselecting a cellular network, the method comprising: activating acellular radio transceiver; determining that, at the time of activationof the cellular radio transceiver, a public land mobile network (PLMN)stored in a subscriber identity module (SIM) does not match a homepublic land mobile network (HPLMN) stored in the mobile; based on thedetermining that, at the time of activation of the cellular radiotransceiver, the PLMN stored in the SIM does not match the HPLMN storedin the mobile device: scanning a most recently used (MRU) frequency listof radiofrequency channels most recently used by the cellular radiotransceiver of the mobile device, said MRU frequency list beingassociated with a previous SIM HPLMN; scanning an old MRU frequency listassociated with a new SIM HPLMN; scanning a likely frequency list pushedor pulled to the mobile device, comprising radiofrequency channelsavailable at a plurality of locations where activation of cellular radiotransceivers is likely to occur, said likely frequency list being for ahome network for the new SIM HPLMN; scanning a likely frequency list fora roaming network for the new SIM HPLMN; and performing a full RAT/bandscan; and selecting the cellular network by identifying one of theradiofrequency channels as a usable channel.
 2. The method as claimed inclaim 1 further comprising: determining if the mobile device was roamingwhen the cellular radio transceiver was deactivated; if the mobiledevice was roaming when the cellular radio transceiver was deactivated,scanning a roaming network likely frequency list; and if the mobiledevice was not roaming when the cellular radio transceiver wasdeactivated, scanning a home network likely frequency list.
 3. Themethod as claimed in claim 1 wherein activating the cellular radiotransceiver is performed by disabling an airplane mode.
 4. The method asclaimed in claim 1 wherein the plurality of locations are airports. 5.The method as claimed in claim 1 further comprising requesting anupdated likely frequency list in response to detecting that the mobiledevice has arrived at an airport.
 6. A non-transitory computer-readablemedium comprising instructions in code which when loaded into a memoryand executed by a processor of a mobile device cause the mobile deviceto: activate a cellular radio transceiver; determine that, at the timeof activation of the cellular radio transceiver, a public land mobilenetwork (PLMN) stored in a subscriber identity module (SIM) does notmatch a home public land mobile network (HPLMN) stored in the mobiledevice; based on the determining that, at the time of activation of thecellular radio transceiver, the PLMN stored in the SIM does not matchthe HPLMN stored in the mobile device: scan a most recently used (MRU)frequency list of radiofrequency channels most recently used by thecellular radio transceiver of the mobile device, said MRU frequency listbeing associated with a previous SIM HPLMN; scan an old MRU frequencylist associated with a new SIM HPLMN; scan a likely frequency listpushed or pulled to the mobile device, comprising radiofrequencychannels available at a plurality of locations where activation ofcellular radio transceivers is likely to occur, the likely frequencylist being for a home network for the new SIM HPLMN; scan a likelyfrequency list for a roaming network for the new SIM HPLMN; and performa full RAT/band scan; and select the cellular network by identifying oneof the radiofrequency channels as a usable channel.
 7. Thecomputer-readable medium as claimed in claim 6 further comprising codethat causes the mobile device to: determine if the mobile device wasroaming when the cellular radio transceiver was deactivated; if themobile device was roaming when the cellular radio transceiver wasdeactivated, scan a roaming network likely frequency list; and if themobile device was not roaming when the cellular radio transceiver wasdeactivated, scan a home network likely frequency list.
 8. Thecomputer-readable medium as claimed in claim 6 wherein activating thecellular radio transceiver is performed by disabling an airplane mode.9. The computer-readable medium as claimed in claim 6 wherein theplurality of locations are airports.
 10. The computer-readable medium asclaimed in claim 6 further comprising code for requesting an updatedlikely frequency list in response to detecting that the mobile devicehas arrived at an airport.
 11. A mobile device comprising: a processorcoupled to a cellular radio transceiver for activating the cellularradio transceiver and for determining that, at the time of activation ofthe cellular radio transceiver, a public land mobile network (PLMN)stored in a subscriber identity module (SIM) does not match a homepublic land mobile network (HPLMN) stored in the mobile device; and amemory coupled to the processor for storing a plurality of most recentlyused frequency lists of radiofrequency channels most recently used bythe cellular radio transceiver of the mobile device and for storing aplurality of likely frequency lists pushed or pulled to the mobiledevice, comprising radiofrequency channels available at a plurality oflocations where activation of cellular radio transceivers is likely tooccur; wherein the processor is configured to: based on the determiningthat, at the time of activation of the cellular radio transceiver, thePLMN stored in the SIM does not match the HPLMN stored in the mobiledevice: scan a most recently used (MRU) frequency list associated with aprevious SIM HPLMN; scan an old MRU frequency list associated with a newSIM HPLMN; scan a likely frequency list for a home network for the newSIM HPLMN; scan a likely frequency list for a roaming network for thenew SIM HPLMN; perform a full RAT/band scan; and select the cellularnetwork by identifying one of the radio frequency channels as a usablechannel.
 12. The mobile device as claimed in claim 11 wherein theprocessor is configured to: determine if the mobile device was roamingwhen the cellular radio transceiver was deactivated; if the mobiledevice was roaming when the cellular radio transceiver was deactivated,scan a roaming network likely frequency list; and if the mobile devicewas not roaming when the cellular radio transceiver was deactivated,scan a home network likely frequency list.
 13. The mobile device asclaimed in claim 11 wherein the cellular radio transceiver is activatedby disabling an airplane mode.
 14. The mobile device as claimed in claim11 wherein the plurality of locations are airports and wherein theprocessor causes the mobile device to request an updated likelyfrequency list in response to detecting that the mobile device hasarrived at an airport.
 15. The mobile device as claimed in claim 11wherein the processor is configured to: define a list of most recentlyused (MRU) frequencies that are specific to a particular combination ofa public land mobile network (PLMN) and a subscriber identity module(SIM); store said list in the memory; and in response to detectingactivation of the cellular radio transceiver, scan said list.
 16. Themobile device as claimed in claim 11 wherein the likely frequency listis downloaded in response to a list update trigger.
 17. The mobiledevice as claimed in claim 11 wherein the likely frequency list ishardcoded.